Though there is no compulsory qualification to become a celebrity PR agent, studies in Bachelor of Mass Media (BMM) helps one understand the profession better.
One could also intern with a Bollywood PR agency or join a PR firm on a trainee level to learn the ropes.
Celebrity publicists are also expected to be good at content writing, as nowadays their main job revolves around creating news content and then disseminating it to news editors and journalists of New-Age websites on the internet.
While most Legacy websites and Veteran websites are doing a lot of paid news, New-Age websites still carry organic content from PRs.
NOTE: Here is a detailed article on the internet explaining the difference between Legacy websites, Veteran websites and New-Age websites.